1. Field of the Disclosure
This specification relates to a polarizing plate, a liquid crystal display (LCD) device having the same, and a method of fabricating the polarizing plate, and more particularly, to a polarizing plate having an anti-glare/reflection layer, an LCD device having the same, and a method of fabricating the polarizing plate.
2. Background of the Disclosure
As the interest in information displays and demands on the use of portable information media increase, research and commercialization are focusing mainly on flat panel displays (FPDs) which are light in weight and thin in thickness. Specifically, a liquid crystal display (LCD) device among such FPDs is a device for displaying an image using optical anisotropy of liquid crystals, and is actively applied to notebook computers or desktop monitors in terms of resolution, color reproduction and image quality thereof.
The FPD includes an anti-glare layer that is located on the outermost surface thereof to reduce reflectance using the principle of optical interferometry, in order to prevent deterioration of contrast and visibility caused due to reflection of incident light entering from outside and a reception (output) of a reflected image.
Among those FPDs, an LCD device is driven by two electrodes facing each other, and a liquid crystal layer interposed between the two electrodes. Liquid crystal molecules of the liquid crystal layer are driven by an electric field which is generated by applying a voltage to the two electrodes.
The liquid crystal molecules have polarization properties and optical anisotropy. The polarization property refers to that electric charges within liquid crystal molecules are concentrated onto both sides of the liquid crystal molecules when the liquid crystal modules are placed within an electric field, and accordingly an arrangement direction of the molecules changes according to the electric field. The optical anisotropy refers to changing a path or polarized state of emitted light according to an incident direction or polarized state of incident light based on a thin and long structure of the liquid crystal modules and the arrangement direction of the molecules.
Accordingly, the LCD device includes as an essential constituting element a liquid crystal panel formed by a pair of transparent insulating substrates, which face each other with the liquid crystal layer interposed therebetween and include electric field generating electrodes, respectively. The arrangement direction of the liquid crystal molecules is artificially adjusted by changing the electric field between the electric field generating electrodes and various images are displayed using transmittance of light which changes during the adjustment of the arrangement direction.
Here, polarizing plates are located on both upper and lower portions of the liquid crystal panel. The polarizing plates serve to decide a transmission degree of light according to disposition of transmission axes of the two polarizing plates and an arrangement characteristic of liquid crystals in a manner of allowing polarizing component light which is aligned with the transmission axes to transmit therethrough.
FIGS. 1A and 1B are exemplary views illustrating the characteristic of light transmitting through a liquid crystal panel.
As illustrated in FIGS. 1A and 1B, a typical LCD device includes a liquid crystal panel P and a backlight unit (not illustrated) provided at a rear surface of the liquid crystal panel P to supply light.
Here, the liquid crystal panel P includes first and second substrates 10 and 5 bonded to each other with a liquid crystal layer 30 interposed therebetween, and first and second polarizing plates 50a and 50b attached onto outer surfaces of the first and second substrates 10 and 5, respectively.
Although not illustrated, on an inner surface of the first substrate 10 are provided with a plurality of pixels each having a transparent pixel electrode, and thin film transistors (TFTs) each controlling an ON/OFF of a liquid crystal driving voltage transferred to each pixel electrode. On an inner surface of the second substrate 5 are provided with color filters for reproducing colors and common electrodes.
The liquid crystal layer 30 interposed between the first and second substrates 10 and 5 has a twisted nematic (TN) mode. Namely, when a voltage is not supplied, an alignment direction of liquid crystal molecules of the liquid crystal layer 30 is twisted by an azimuth angle of 90° from the first substrate 10 to the second substrate 5 while a major-axial direction of the molecules is in parallel to the first and second substrates 10 and 5. Here, polarization axes of the first and second polarizing plates 50a and 50b are orthogonal to each other.
The liquid crystal panel P does not emit light by itself and thus the backlight unit which supplies light to the liquid crystal panel P is located at the rear of the liquid crystal panel P.
With the configuration of the liquid crystal panel P, as illustrated in FIG. 1A, when a voltage is not supplied (Off state), the first polarizing plate 50a allows for transmission therethrough of only linearly-polarized light aligned in parallel to the polarization axis of the first polarizing plate 50a, of light emitted from the backlight unit, while absorbing the other light.
While transmitting through the liquid crystal layer 30, the linearly-polarized light is rotated by 90° according to the azimuth angle of the first polarizing plate 50a and thus transmits through the second polarizing plate 50b, thereby reproducing a white color.
Next, when a voltage is supplied (On state), the liquid crystal molecules of the liquid crystal panel P, as illustrated in FIG. 1B, are aligned in a manner that the major axis thereof is perpendicular to the first and second polarizing plates 50a and 50b. Therefore, optical rotary power of 90° vanishes, and linearly-polarized light transmitted through the first polarizing plate 50a is blocked by the second polarizing plate 50b, thereby reproducing a black color.
The second polarizing plate 50b includes an anti-glare layer (not illustrated) to prevent glare caused due to incident light entering from outside. Light incident onto the second polarizing plate 50b is diffused and scattered by diffused reflection due to the anti-glare layer.
The second polarizing plate 50b is further subject to a surface treatment through anti-reflection sputtering in order to reduce reflectance of incident light entering from outside. In other words, an anti-reflection layer is formed by alternately coating (stacking) two inorganic films having different refractive indexes on the anti-glare layer into five or six layers.
Here, the anti-reflection layer cannot be fabricated by wet coating due to roughness of a surface of the anti-glare layer, and rather fabricated by several times of sputtering as dry coating.
In this manner, the fabrication of the conventional polarizing plate brings about an increase in costs due to high-priced inorganic film materials and plural-time sputtering processes. Also, the polarizing plate has a magenta color in all directions due to the multi-layered structure.